High integration of a semiconductor integrated circuit such as MPU or DRAM and miniaturization required for the high integration of the semiconductor integrated circuit have been realized by a technology of shortening wavelength in an optical system of the exposure equipment for transferring a circuit pattern, and a technology of a liquid immersion, a multiple patterning and the like.
Although it is said that shortening of wavelength in the optical system has been approaching the technological limit, in recent years, an EUV (Extreme Ultra Violet) exposure equipment is being put to practical use. Heretofore, shortening of wavelength has been developed gradually over several decades from 365 nm through 248 nm to 193 nm (currently). However, the EUV (Extreme Ultra Violet) is a technology for advancing the shortening of wavelength straight to 13.5 nm, and thus the EUV has various technological hurdles that need to be overcome.
One of the technological hurdles is a measure for pollution control within the apparatus. The EUV exposure equipment is a super-precision equipment, and particularly performance of the EUV exposure equipment is drastically lowered by entry of a foreign matter into the optical system. The EUV exposure equipment comprises a light source unit for emitting an EUV, and an exposure unit for exposing wafers with the EUV emitted from the light source unit. It is known that oxide of tin (Sn) produced by irradiation of laser onto a target in the light source unit and organic material separated from light-sensitive material (resist) in the exposure unit are typical contamination sources. Because these oxide and organic material are inevitably produced by the operation of the apparatus, they cannot be prevented from being produced.
As a measure against these contamination sources, there is a method of using a hydrogen gas. The oxide of tin is removed as gaseous hydride by using the hydrogen gas at a rate of several hundred liters per minute (L/min) in the light source unit, and the organic material is gasified and removed by using the hydrogen gas at a rate of several dozen liters per minute (L/min) in the exposure unit. Although the used hydrogen gas is mostly unreacted, such hydrogen gas is discharged from the apparatus as a carrier of the removed contaminant. In this case, the discharged hydrogen gas varies greatly in amount depending on the presence of operation process for evacuating the exposure unit to produce a vacuum therein, independent operation of the light source unit and the exposure unit, respectively, at some level, or periodic maintenance.
Therefore, a processing gas (exhaust gas) containing the hydrogen gas which has a fluctuation range from a hundred and several tens liters per minute (L/min) to several hundred liters per minute (L/min) is discharged from the EUV exposure equipment.
The processing gas (exhaust gas) discharged from the manufacturing apparatus for manufacturing semiconductor devices or the like is generally introduced into an exhaust gas treatment apparatus where the exhaust gas is treated and made harmless, and is then emitted into the atmosphere. As this treatment method for making the exhaust gas harmless, as disclosed in Japanese Patent No. 4937886 or the like, there has been widely used a combustion-type exhaust gas treatment apparatus in which a fuel (fuel gas) and an oxidizing gas (oxygen-containing gas) are mixed to combust the fuel and to form a flame, and a processing gas (exhaust gas) is mixed with the flame to perform combustion treatment of the processing gas.
However, the processing gas (exhaust gas) discharged from the EUV exposure equipment contains a large amount of hydrogen gas, and thus there is a possibility that the processing gas can be treated by combustion only by supplying the oxidizing gas (oxygen-containing gas) without supplying the fuel.
Hydrogen has characteristics of a fast combustion speed and a wide combustion range (being combustible even in high concentration and in low concentration) particularly among combustible gases. Therefore, there is a possibility that hydrogen is rapidly combusted to form a local high-temperature part immediately after it flows into a combustion chamber, thus causing heat damage of the combustion chamber. As an inflow amount of hydrogen is larger, the possibility of heat damage of the combustion chamber is higher. As a common practice, the heat damage can be prevented by using a large amount of oxidizing gas (air) and combusting hydrogen. However, in this case, a combustion chamber having a large capacity is required and an amount of combustion gas increases, resulting in a large-size apparatus. Further, it is necessary to adjust an amount of the oxidizing gas to a flow rate of hydrogen. This is because when a small amount of hydrogen gas is mixed with a large amount of oxidizing gas and is combusted, if the concentration of hydrogen gas is lower than a lower limit of combustible concentration (in the case of air-hydrogen mixture, hydrogen concentration is 4%), the hydrogen gas cannot be combusted.
However, because the flow rate of hydrogen varies according to operating condition of the EUV exposure equipment, it is difficult to adjust the amount of oxidizing gas to the flow rate of hydrogen. Therefore, it is necessary to combust a large amount of hydrogen by a minimum necessary amount of oxidizing gas, and thus it is necessary to take a measure against the heat damage of the combustion chamber.
As a combustion method which can combust a processing gas (exhaust gas) containing a large amount of hydrogen discharged from the EUV exposure equipment and has a potential capable of preventing heat damage of the combustion chamber, the present inventors have conceived a thermally-insulated mixed combustion method in which a cylindrical mixed flame of a mixture of two kinds of gases which is distant from the inner wall of the combustion chamber is formed by blowing a processing gas containing hydrogen and an oxidizing gas into the combustion chamber, respectively, in a tangential direction to the inner circumferential surface of the combustion chamber.